(1) Field of the Invention
The present invention relates to an optical output power automatic attenuation circuit for monitoring the disconnection and the erroneous connection of optical fibers in an optical communication apparatus to prevent a light of high power from being emitted to the outside.
(2) Related Art
FIG. 15 is a configuration diagram showing one example of a typical optical communication system. This optical communication system is configured such that a transmission side terminal apparatus 110 and a reception side terminal apparatus 120 are connected to each other by a transmission path 130 laid on the seated or the like, and also a plurality of repeaters 140 is arranged on the transmission path 130. In the transmission side terminal apparatus 110, a plurality of optical signals of different wavelengths output from an optical sender (OS) 111 is multiplexed by a multiplexer 112 to become a wavelength division multiplexed (WDM) light, and the output power of the WDM light is controlled by an optical amplifier 113 and a supervisory control section 114 so that the input power to the repeater 140 reaches a required level, to be output to the transmission path 130.
FIG. 16 is a configuration example of a conventional optical amplifier disposed in the terminal apparatus or the repeater of the optical communication system as described above. In the optical amplifier of FIG. 16, a WDM light input to a signal light input terminal TsIN of an amplifier board 210 is propagated sequentially through erbium-doped fibers (EDF) 211 and 212 serving as amplification media. Pumping lights Lp respectively output from a plurality of booster boards 220A to 220C, and 220A′ to 220C′ are injected to the EDFs 211 and 212 via pumping light input terminals TpA to TpC and TpA′ to TpC′. Thus, the WDM light Ls is amplified when passing through the EDFs 211 and 212, to be output from a signal light output terminal TsOUT. At this time, as the pumping light Lp supplied to the amplifier board 210 from each of the booster boards 220A to 220C and 220A′ to 220C′, there is used a laser light belonging to the hazard class 3B in conformity with IEC 60825 which is the International standards of laser products, CENELEC standards (EN60825-1), and JIS standards (JISC6802). Therefore, in the case where any one of optical fibers, which are connected respectively from the respective booster boards 220A to 220C and 220A′ to 220C′, to the pumping light input terminals TpA to TpC and TpA′ to TpC′, is artificially pulled out, the high power pumping light Lp of the hazard class 3B is emitted into the air. In such a case, on the laser standards described above, there is required the safety designing to attenuate the pumping light Lp to the safety level such as the hazard class 1 at which a human bodies are not affected by the pumping light Lp.
FIG. 17 is a diagram showing an essential configuration of a conventional optical amplifier provided with an optical output power automatic attenuating function. As shown in the left side of FIG. 17, if an optical fiber connected from a booster board 220 to an amplifier board 210 is pulled out from a pumping light input terminal Tp, the pumping light Lp is not received by an optical coupler 215 and a light receiver (PD) 216 which are disposed on the amplifier board 210 side for monitoring the pumping light Lp input to the amplifier board 210, and an electric signal Sm indicating information of the non-reception is transmitted from the light receiver 210 on the amplifier board 210 side to a level monitoring circuit 223 on the booster board 220 side. The level monitoring circuit 223 recognizes that the optical fiber is not connected in the case where the light receiving level of the light receiver 216 reaches a threshold or less, and transmits information of disconnection to a LD control circuit 222. The LD control circuit 222 controls a pumping light source (LD) 221 so that an output from the pumping light source 221 becomes the safety level, in accordance with the information from the level monitoring circuit 223. Then, as shown in the right side of FIG. 17, when the optical fiber from the booster board 220 is connected to the input terminal Tp of the amplifier board 210, the light receiver 216 in the amplifier board 210 receives the pumping light Lp of the safety level, so that information of the reception is transmitted via the electric signal Sm to the level monitoring circuit 223 on the booster board 220 side. In the level monitoring circuit 223, the connection of the output fiber is recognized based on the light receiving level of the light receiver 216, and information of the connection is transmitted from the level monitoring circuit 223 to the LD control circuit 222, so that the pumping light source 221 outputs the pumping light Lp of the normal operational level. As described above, in the conventional optical amplifier, there has been applied a function (closed loop control) of automatically attenuating and returning the output level of the pumping light source 291 by the disconnection and connection of the optical fiber, to perform the safety measure.
A submarine cable communication enables an economic construction of a large capacity transmission system by applying an optical amplification repeating technology, and serves an important role as means for data communications such as the Internet and the like, and also means for international internal communication for which demands are increased. However, in order to realize the long distance and large capacity transmission, it becomes necessary to design an in-line amplifier to have the high power, and accompanied with this, an increase in the pumping light output level from the booster boards, an increase in the numbers of booster boards and the like will be expected in the future. Therefore, there is a demand for the establishment of the safety designing for the high power output.
To such a demand, the dosed loop control applied to the above described conventional optical amplifier has a problem in that there is a possibility that the pumping light of high power is erroneously emitted into the air in the case where the optical fiber is erroneously connected.
Namely, as shown in FIG. 18 for example, it is provided that a connection end of an output fiber of a booster board 220A to an amplifier board 210 is disconnected, and a connection end of an output fiber of a booster board 220B to the amplifier board 210 is erroneously connected to a pumping light input terminal TpA on the booster board 220A side. In such a case, if the attention is made on the booster board 220B side, since a pumping light input terminal TpB is in a disconnection state, a light receiver 216B in the amplifier board 210 does not receive the pumping light Lp, and information indicating the non-reception state is transmitted from the light receiver 216B to a level monitoring circuit 223B of the booster board 220B. The level monitoring circuit 223B recognizes that the optical fiber is not correctly connected to the pumping light input terminal TpB, according to the information from the light receiver 216B, to transmit the recognition result to a LD control circuit 222B. As a result, the LD control circuit 222B controls a pumping light source 221B so that an output of a pumping light source 221B becomes the safety level.
On the other hand, on the booster board 220A side, a light receiver 216A in the amplifier board 210 receives a light of safety level from the booster board 220B, and information indicating the light receiving state is transmitted from the light receiver 216A to a level monitoring circuit 223A of the booster board 220A. The level monitoring circuit 223A erroneously recognizes that the optical fiber is correctly connected to the pumping light input terminal TpA, according to the information from the light receiver 216A, to transmit the recognition result to a LD control circuit 222A. The LD control circuit 222A controls a pumping light source 221 A so that an output of the pumping light source 221 A becomes the normal operation level. As a result, there is a possibility that the pumping light of high power belonging to the hazard class 3B is emitted into the air.
In order to solve the above problems related to the conventional dosed loop control, as shown in FIG. 19 for example, in a transmission section (for example, transmission terminal station) 300, there are disposed a transmission side ID generating section 301 that generates connection management information (ID), and a transmitted light control section 302 that switches a transmitted light to the connection management information generated in the ID generating section 301 according to an erroneous connection monitoring request Further, in a reception section (for example, a wavelength division multiplexing apparatus) 310, there are disposed a photoelectric converting section 311 that receives the connection management information from the transmission side, a reception side ID generating section 312 that generates connection management information corresponding to the transmission side, and a judging section 313 that judges whether or not the connection management information received by the photoelectric converting section 311 is coincident with the connection management information generated in the reception side ID generating section 312. Thus, it is effective that the known technology which realizes the detection of erroneous connection of the optical fiber between the transmission section 300 and the reception section 310 (refer to Japanese Patent No. 3478247, Japanese Unexamined Patent Publication No. 2001-358657 and Japanese Unexamined Patent Publication No. 5-134790) is applied to the dosed loop control of the optical amplifier.
However, in the case where the know technology as described above is applied to the dosed loop control of the optical amplifier, the configuration is such that whether or not the connection management information transmitted from the transmission section 300 to the reception section 310 is correct is judged on the reception section 310 side. Therefore, in the configuration of the optical amplifier as shown in FIG. 16, if the number of booster boards 220 corresponding to the transmission section 300 is increased, there is caused a problem in that the circuit scale of the amplifier board 210 corresponding to the reception section 310 is enlarged according to the number of booster boards. Further, since the judgment of the connection management information in the reception section 310 is performed using the connection management information generated in the reception section 310 as an expected value, there is a drawback in that the management of the connection management information to be transmitted and the management of the connection management information which becomes the expected value for the judgment on the reception side should be doubly performed.